Talked to Performance Cat about my nacra 450 cracks. See other posts. They said they'd do things about the same as Eric suggested, except using 2 layers of Knytex instead of 3 layers of cloth. They also said this was an uncommon problem. Long ago they did have an issue with this. Not when my boat was made. They figured the boat must have rammed something. When I got to looking closer, I did notice gelcoat cracking (crazing?) around both bow cracks. That's the pic here. I'll continue after uploading...

So I bought a used DeWalt 421 5" orbital sander. With a 80 grit disc, I ground off the gelcoat and into the resin. I didn't see any fibers after a little bit, so I hand filed down in one spot till I started getting into white colored stuff again. The pic here shows that. Directly below this whitish area in the picture you can see the original crack, partly filled with white gelcoat dust...

There's no core in this area. Never saw a flange or anything. So I was a bit surprised to see that this 'whitish' area was the inside layer of glass. Poked through with a probe and was inside the hull. I opened up the rest of the crack that widened when I pried between the hull halves. That left about 6" on either end of the opened area.

So my plan is to put a lot more epoxy mixed with ?? in the 1/4" gap, then clamp. Then, in a day or 2, I'll lay up the knytex. I'm also getting white pigment, which hopefully will replace painting of gelcoating.

I also notice the inboard hull half is thicker than the outboard. And the crack didn't run right inbetween the 2 halves, rather was in the thicker (inboard) half.

Here's a pic of how it looks now. Lemme know what you think.

Cheers,
Danno

Took that orbital back and got a angle grinder with 40 grit disc. Very easy to take off too much now, but I managed. What do you guys use?

The first hull now has a 1/4" x 9" long gap in it. Moved the cat into my garage and am drying it out with a blower T-ed to both drain holes. Plenty of air moving out the bow cracks now. Douched cracks with acetone too and wedged smaller cracks open with nails. Continued after pic post...

And I did find the flange. It extends up from the bottom on centerline about 2". Both hulls had cracks that were on the outboard side of this flange. The first hull has a 1/4" gap bound by the flange on one side, the outer hull on the other. So I stuffed black foam (eps?) about an inch into the crack to make a backing for the epoxy.

I bought a strip of 9oz tape, cuz the hardware store doesn't have chopped strand or milled fibers. That would have been my choice for a filler, according to what I've read. So now I can cut off a piece of tape and stuff it into the gap, sort of accordian style, then pour in the epoxy. If I do this, would it be best to thicken it with silica filler, in case the foam backing fails or absorbs too much?

The other idea is to cut up the tape into small pieces, making a chopped strand immitation.

I'll have the blower going for 12 hours straight and will tackle the gap/crack epoxy in the morning. Then 36 hrs after that, I'll lay up the knytex. Which reminds me...

So far I've gone easy on grinding down the glass where the tape layers are to go (not the crack/gap repair). I've got the gelcoat and a bit of the resin/glass removed for about 2" on either side of the skeg. On the one hand I'm afraid of taking off too much, making a hole. On the other hand if I don't take off much more than the gelcoat, it would be hard to make a smooth transition from the new to the old, right?

Cheers,
Danno

PS: pic here is of the first hull w/ 1/4" gap. 2nd hull I was more careful and opened up the crack about 1/16" by hand sawing it (coping saw?). Plan on squirting epoxy directly into crack.

I was just wondering how will you get your hulls to its original shape???
I have N6.0na and I have to restore some fiberglass and gel coat.
Any hints how to shape your hulls back to be the same as factory or anywhere close to its original shape?

Kris

Good question. I'm new to working with glass. The basic shape hasn't changed much. I took off maybe 1/8-3/16" in thickness in most places. Not smooth by any means, now. Unless I come up with something else, I'll just use a squeegee and eyeball it. As you may have seen, I ground down probably too much on the very bottom of the first hull, making a 1/4" gap. I filled that in as planned this morning. This evening I built up on top of that, making the wedge shaped bottom part out of epoxy and silica. Smoothed it out fairly roughly with a spatula/squeegee.

Pic here shows that first bow after the second epoxy job. You can see the white silica filled epoxy. It's replacing what I ground away. Next step is laying up the Knytex. After that, I imagine I'll have to come back and put a coat or 2 of epoxy, I suppose by brushing it on. Not sure how it's gonna level out, since it's on a vertical surface. Might have to thicken it a bit, maybe drag the squeegee over it. Dunno yet.

If this does or would look like crap, I'm thinking of just painting. I've heard polyurethanes might do well. Gelcoat is another possibility.

Take care,
Danno

Remember that whatever the surface looks like before gelcoat will be the same that it looks after. So sand it down and use filler and sand again with about 100 grit before gelcoating. Use basic gelcoat and let it sit for about 10 minutes and then spray on PVA mold release over the top. This will seal the gelcoat so that it will all set up perfectly. You can then in about 24 hours just wash off the PVA mold release and finish touchup sanding and polishing.

Mike Hill
Tiger #1520

Thanks, Mike.

Just talked to a local glass guru. He suggested using resin w/ microballoons on the roughly ground glass now, then sand to prep for the glass placement. Sounds like what you're saying.

Cheers,
Danno

Danno,
To fill the hole like you have made, I have made a backing plate for a fiberglass patch to go INSIDE the hole. I haver done this successfully by finding softer plastic material (like the side of a PVC bleach bottle with about the right curve. I put 2 small holes in the middle 3-5 inches apart and run a copper wire or heavy string thru the holes to the outside, tie into loops:
This patch backing can be bigger and longer than the hole because it is inserted sideways then twisted to fit the hole. Once you have tried it and are confident that you can get it in, pulled up and fits well, then you pull on the strings to pull your patch backing into place. Hold it there with a "strongback"- another piece of wood on the outside, placed across the hole lengthwise thru the loops.

The sanding is all done on the INSIDE edges of the hole, right?
Cut fiberglass cloth to fit (big enough to overlap the hole edges inside). Place 2 or 3 layers of fiberglass cloth on the backing plate (thread the string thru the cloth). Now use epoxy thickened with fumed silica dust or microballoons -& smear some inside the hole. Now wet out the cloth, turn the patch to insert into the hole, position it and pull up into place. Tie wires or string over the "strongback" to hold it up tight (engage wife for enough hands after being sure she has gloves on too)- and stick a wedge under the strongback to get it all JUST tight enough.

If you make a mess of it by dropping the patch or getting it all crooked, have another patch assembly ready to use. With epoxy you have enough time.

When this is all pretty hard the next day, it will fill the hole but allow you to sand a little (cut the wire or string & pull out). Fill by adding cloth pieces to the top of the hole, and overlapping the outside = A VERY strong repair.
Leave the PVC backing inside.

That is very good repair advice. the backing plate is a good idea. Some other suggestions: make a backing plate of fiberglass, don't use aerosil or cabosil as a filler as it is too hard and brttle. use milled fibers and/or a liteweight filler for the bog. use carbon instead of glass if you can. make sure the surrounding area is ground down enough so that, say 4-6 layers of 6oz. won't buldge up above the original contour. when glassing the outside you can strech plastic over the repair using tape as a poorman's vacumebag. that makes a smooth finish and a tight lam. Also tape of the repair area so it doesn't grow as you work.
hope this helps.

Thanks guys :-)

Dacarls: I'll keep that backing plate info for the next time, since I've already past that. Not sure what you mean by 'sanding on the inside edges'.

JR: vacuum bagging: can you give me more info? What type of tape? Also, taping off the repair area so it doesn't grow?

So ended up mixing "Micro-Fine precipitated silica" with microballoons and spread it over the exposed rough glass. Sanded it down, then draped a 1" wide layer of Knytex over either side. Had to abandon this, cuz it kept springing up off the hull. Too skinny for something like Knytex. It's got mat, then 2 layers of yarn. If I would have wet out a 2" at the same time, maybe could have gotten it to lay flat. So I chucked it and went with a 2" wide piece. Worked okay. Used some white pigment and came out close to the same color. After this dried 5hrs, I put on a 3.5" wide strip on top of it on one hull so far.

Spreading on the epoxy/filler to make smooth surface was useless. The knytex was so thick that it spanned any unevenness in the roughly ground fiberglass hull.

I wasn't sure if I was putting enough resin on the fabric. So I made sure it ran down the sides a little. Figured if this happens after I squeegee or roll it, then there is a bit more than needed to saturate it.

Planning on putting a little thickener into the resin, then brushing it over the first knytex layer to fill the gaps between the outer yarn layers. Then lay the dry fabric on and wet it out.

Pic here is of the first knytex layer.

Cheers,
Danno

This pic is right after the second knytex layer. There's very little room between the existing gelcoat and the end of the knytex. Plan is to mix some microballoons, silica, pigment, and resin together and coat all my new glass work plus blend into the gelcoat. There's still time for suggestions, cuz I'm laying up the 2nd layer on the 2nd hull first.

Take care,
Danno

PS: You can see the orange blush from when I first started this project a couple weeks ago. Thick epoxy curing outside in 50 degree weather. Should buff or sand off, right?

See if you can't find someone to paint your hulls with IMRON. My friend has a catamaran rental business and is slowly getting all his boats painted with this. It is a very strong paint!

Whan adding bog (epoxy with microballoons or carbon) as filler, cover with fairly stiff but flexible plastic to get it level and smooth- taped down. Epoxy won't stick to polyethylene (visqueen): if you aren't sure, tape down a thin sheet of shopping bag polyethylene or painters' drop cloth first.

Q: Why sanding inside the edge of the hole? So that a flexible backing plate (greenhouse fiberglass sheet glazing is good) covered with wetted-out 6 oz cloth layers will stick snugly and well to the inside of the hole. Then it will be recessed just enough to fill from the outside with maybe 3 more layers and be very strong.

Thanks, Dave.

Understand the 'inside sanding' now.

For the epoxy, I chose to just squeegee it on and let it air dry. Mixed it as planned and spread it around with a squeegee. I'll sand it smooth. The color will be off a bit. Could do the polyurethane paint thing. It would be hard to get a color match. The only place locally that sells 2 part poly is a marine store that doesn't mix paint. It would be $50 for the paint, $25 for the epoxy barrier coat. Would a paint store be able to match 3rd party poly? Or would I be able to do that? The pigment I have mixed with the epoxy is too white, at least compared to the top layer of gelcoat. I did notice while grinding that the gelcoat underneath was a bit brighter. And the hulls hadn't been cleaned recently.

Or what would happen if I just sanded smooth and left it like it turns out? Tackle the paint/color job later?

Take care,
Danno

Danno,

Another thing to keep in mind is that most epoxies do not hold up to UV very well. Some have UV inhibitors that help with that but epoxy will tend to turn yellow unless it's made specifically for an exterior coating application.

If your looking for temorary quick paint a spray can of acrylic works just fine, and to be honest, its hard to tell that thats all it is.

Thanks, guys.

I put pigment in the epoxy. There was a UV blocking concentration I'm sure I exceeded. The only place I didn't put it was on the original fix, along the bottom. But that won't see any UV.

Yeah, a cheapo paint match for this little area is what I was leaning toward. If it rubs off, I'll put it on again.

Ciao,
Danno

Got the cat outside now. I put the last epoxy on Wednesday evening, let it stay in the 70 degree garage for 12 hours afterwards. Been sitting in 50 degree air since then. How long do I have to wait for it to be safe to sail? Somebody mentioned a few days, I think, but can't find that response.

Take care,
Danno